A memory cell, such as a dynamic random access memory (DRAM) cell, conventionally includes a charge storage capacitor coupled to an access device, such as a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET). The MOSFET functions to apply or remove charge on the capacitor, thus affecting a logical state defined by the stored charge. The conditions of DRAM operation, such as operating voltage, leakage rate and refresh rate, will, in general, mandate that a certain minimum charge be stored by the capacitor.
Capacitors include two conductors, such as parallel metal or polysilicon plates, which act as electrodes. The electrodes are insulated from each other by an interposed dielectric material. One type of capacitor used in DRAM cells is a metal-insulator-metal (MIM) capacitor. The dielectric constant, k, of the dielectric material (i.e., insulator material) in the capacitor is a crucial element for mass-producing DRAM cells. For example, a 3× nm DRAM cell or larger requires a dielectric material having a dielectric constant of at least about 55 in order to achieve the desired capacitance.
In certain capacitor configurations, such as pillar-type capacitors, ruthenium is deposited as a bottom electrode in direct contact with a polysilicon material, which functions as a sacrificial material in the pillar capacitor. The ruthenium and polysilicon may react, forming ruthenium silicide (RuSi). When RuSi is present at an interface between titanium dioxide (TiO2) and the ruthenium, the RuSi may cause high current leakage of the capacitor, which decreases the efficiency of the capacitor.
Crystalline dielectric materials tend to have a higher dielectric constant than amorphous dielectric materials. For example, rutile titanium dioxide (TiO2) has a dielectric constant of about 170 along the c-axis of the crystal structure and a dielectric constant of about 90 along the a-axis of the crystal structure, while amorphous TiO2 has a dielectric constant of about 30. However, forming rutile TiO2 often requires the use of high temperature processes. For example, anatase TiO2 may be converted to rutile TiO2 by annealing the TiO2 at a temperature of at least about 800° C. However, such increased temperatures may cause damage to other components of the capacitor or device in which the capacitor is incorporated. Accordingly, low temperature methods of forming rutile TiO2 for use in capacitors are desirable.